Loud speaker baffle having improved low frequency reproduction characteristics



y 1961 B; w. LOWELL 2,982,372

LOUD SPEAKER BAFFLE HAVING IMPROVED LOW FREQUENCY REPRODUCTION CHARACTERISTICS 2 Sheets-Sheet 1 Filed May 16, 1957 May 2, 1961 B. w. LOWELL 2,982,372

LOUD SPEAKER BAFFLE HAVING IMPROVED LOW FREQUENCY REPRODUCTION CHARACTERISTICS Filed May 16, 1957 2 Sheets-Sheet 2 RESPO refod ucv w CYCLES PER 5c0-0 I000 FR E I JUENCY IN CYCLES PEI? SECOND RESPONSE II 05 I000 F5ZQUENCV IN CYCLES PER SECO D INVE A/TOQ: BENJAMIN w. AOWEL L LOUD SPEAKER BAFFLE HAVING IMPROVED LOW FREQUENCY REPRODUCTION CHARAC- TERISTICS Benjamin W. Lowell, 3030 Laclede Station Road,

' St. Louis, Mo.

Filed May 16, 1957, Ser. No. 659,621 3 Claims. (Cl. 181-31) for afiixation to walls, ceilings, and the like, to provide 2 for a front mounting of the speakers and for convenient installation.

It has been found that in loud speaker installations employing such bafiles and protective enclosures for the speakers that the bass frequencies are undesirably mufiled or distorted or even completely lost. These frequencies are in the general range of 40 to 200 cycles. The protective enclosure around the rear of the speaker is believed to form a pressure chamber in which there is no release for the pressure waves built-up by the vibration 3 of the speaker cone and as a result of which the cone or diaphragm cannot vibrate properly due to the dampening efiect of the pressure chamber. Such vibrations and distortion of the sound waves in the sealed space between the protective enclosure and the speaker have prevented the faithful transmission of'low bass frequencies and have otherwise distorted the true sound waves which are desired to be reproduced.

By means of the instant invention it has been found that the bass frequencies can be faithfully reproduced by relieving the sound wave pressure between the protective enclosure and the speaker in the construction of the novel baflle of this invention. In essence the speaker baffie of this invention provides for a pressure relief and sound transmission through slots around the periphery of the baifie forming the frame between the front of the protective enclosure and the speaker. For best results these slots are located closely adjacent the speaker opening in order to provide substantially uniform sound distribution. Any tendency to cause the build-up of pressure or sound waves within the speaker and the protective enclosure area is obviated by dissipation through the openings in the baflie.

It has further been found that a very high faithfulness of reproduction in the low frequency ranges can be ob- 5 tained through the use of the speaker battle of this invention in association with the loud speaker diffusing cone and baffle mounting shown and described in my Patent No. 2,563,948. Superior tone quality and reproduction and low frequency response are made possible through the combination structure of this invention.

The battle of this invention and thesupporting structure in which it is employed are of particular advantage since the construction and installation-may be made in a similar manner to that previously employed. The bafiles 70 are extremely easy to manufacture and can be made in a number of dilferent forms and embodiments while obnited States Patent 0- Patented May 2, 1961 taiuing uniformly desirable reproduction characteristics.

Accordingly, it is a primary object of this invention to provide an improved loud speaker baflle having very advantageous low frequency reproduction characteristics.

It is a further object of this invention to provide a loud speaker bafile which is adapted to be employed with a loud speaker cone and a protective enclosure in which the baflle is provided with openings to relieve any built-up pressure or sound waves in order to obtain improved reproduction characteristics.

It is still another object of this invention to provide an improved loud speaker bafiie adapted to be used with a loud speaker and a protective enclosure and a loud speaker diffusing cone in which the loud speaker battle has openings to relieve any built-up pressure or sound waves within the space between the protective enclosure and the loud speaker to obtain improved loud frequency reproduction and better bass qualities.

Still another object of this invention is to provide an improved loud speaker baflie which is made of standard materials of construction and is rugged and relatively inexpensive to produce and can be installed in a simple manner.

Further objects of this invention will appear in the detailed description which follows and will be further apparent to those skilled in the art.

In the accompanying drawings there are shown for the purpose of illustration several preferred embodiments of this invention. It is to be understood that these drawings are shown for illustration and example only and that the invention is not limited thereto.

In the drawings: 7

Figure 1 is a plan view of one form of the speaker bafile of this invention;

Figure 2 is a view in cross section taken through an installed speaker, protective enclosure and diffuser cone provided with a loud speaker baifie of the type shown in Figure 1;

Figure 3 is a plan View of a modified speaker bafile and supporting structure construction;

Figure 4 is a view in cross section of the modified loud speaker baffie taken on line 4-4 of Figure 3;

Figure 5 is a view in cross section of a further modification of supporting structure for a speaker bafiie of the types shown in Figlres 3 and 4 which is suspended from a ceiling; and

Figure 6 is a series of 3 charts showing the reproduction characteristics of the speaker and baflle of Figure 5 on the axis, 30 ofl the axis and 60 oi the axis.

One form of the bathe of this invention is indicated by the reference numeral 10 in Figures 1 and 2. It comprises a supporting rim 11 and an annular offset front face 12. A central opening 13 is provided for transmission of sound from the loud speaker. Around the periphery of the face 12 are a number of slotted openings 14 which provide for pressure or sound wave relief as well as transmission of sound waves as will further appear.

In Figure 2 the baffle 10 is shown mounted upon a Wall 20 which will be understood to be either a ceiling or a side wall. The associated structure includes a conventional speaker 21 secured to the inside of the bafiie and a protective enclosure member 22 surrounding the rear of the speaker. It will be seen that the slotted relief openings 14 are disposed between the side of the protective enclosure and the front of the speaker 21 to effectuate the pressure relief.

A diifuser cone 23 is further shown in Figure 3. It is connected to the baffle by supporting rods 24 in the manner shown and described in applicants Patent No. 2,5 63,- 948. It is to be understood that the diffuser cone may be used where desired to provide further improved reproduction characteristics. However, it may be eliminated in certain cases where high fidelity is not critically essential, while still obtaining improved reproduction of bass tones through the slotted openings of the speaker bafiie of this invention.

A further embodiment of the speaker baffie of this invention is shown in Figures 3 and 4. In these figures V the speaker baflie is mounted directly to the wall and the Wall forms a rear sealing enclosure for the baffle with the speaker being mounted Within the space provided by the baffle and the wall as shown in Figure 3. The bafi'le is somewhat in the form of a deep dish of frusto-conical configuration and is generally indicated by the reference numeral 30. The mounting of the speaker and the diffuser cone shown in Figure 3 is similar to that shown in Figure 2 upon the front face of the interior of the speaker bafile. Since the speaker bafile has considerable depth provided by the tapering side walls 31, the wall can be utilized as the rear sealing enclosure to protect against damage of the speaker.

The slotted openings 14- around the periphery of the face of the balfie are the same in construction as described in connection with Figures 1 and 2. It will be observed that these openings are at the same level as the speaker opening and closely adjacent thereto which is important in obtaining optimum sound transmission. In this embodiment the diffuser cone 23 has been shown but again as in other embodiments to be described this may be deleted where desired.

Still a further embodiment is shown in Figure 5. In this embodiment a speaker bafiie 39 is employed similarly as shown in Figures 3 and 4. However, instead of using a wall mounting a protective enclosure 35 is employed. This protective enclosure is mounted to the mounting rim or flange 11 of the speaker baffle 30. The speaker and the diffuser cone are mounted as previously described in the aforementioned embodiments. The entire unit may be suspended by a chain 36 or the like from a ceiling 37. In this embodiment as in previous embodiments convenient sources of electrical connection may be made by wiring to the loud speaker in conventional manner.

Use

The loud speaker bafile 10 shown in the structure of Figure 2 operates very efficiently for reproduction of sound and particularly for improved transmission of low bass frequencies. When sound is transmitted through the loud speaker 21, the loud speaker cone or diaphragm vibrates as is conventionally understood. Any vibration set up will cause the creation of pressure or sound waves within the enclosure between the back of the loud speaker and the protective enclosure 22. In the past, such pressure or sound waves have been trapped which caused distortion of the low bass frequencies.

By Virtue of the instant invention the relief openings 14 permit the escape of any presssure built-up within the enclosure between the loud speaker and the protective enclosure. In this manner the loud speaker 21 can freely vibrate without any restriction. In addition, sound waves are passed through these openings which are combined with the sound waves passing through the central speaker opening to produce optimum sound transmission. As a result the reproduction of sound through the loud speaker is greatly improved in faithfulness and fidelity and the low bass frequencies which have previously been distorted or lost can be transmitted with a high degree of efiiciency. When the diffuser cone 23 is employed, it has been found that further improved characteristics are obtained. Such improved characteristics present an overall faithfulness of reproduction in the low bass frequency and the higher frequency sound range which represent a true advance in sound reproduction.

In the embodiments of the loud speaker bafiie of Figures 3 and 4 there is made possible a sound reproduction by an offset mounting upon a wall or a ceiling which forms the base of the supporting structure. The flat wall 20' encloses the rear of the loud speaker baifle which is in frusto-conical shape to form a protective enclosure and takes the place of the protective enclosure 22 shown in Figure 2. In this structure the loud speaker is protected in a similar manner as previously disclosed while the relief openings 14 provide for the escape of any built-up pressure or sound waves between the loud speaker and the wall 20.

In the embodiment of Figure 5' the improved loud speaker baffle 30 is shown connected to a suspendedunit. In this unit the protective enclosure 35 operates in a similar manner as above-described for the wall 20 and the protective enclosure 22 to seal off the rear of the loud speaker and protect it against any possible damage. The loud speaker baffle 30 operates in the same manner as previously described in connection with Figure 2 and Figure 3 since the relief openings 14 provide for relief of any built-up pressure or sound waves between the space defined by the baffies side walls and the speaker and the protective enclosure 35.

By virtue of the instant invention a loud speaker baffie has been provided which makes possible the reproduction of low bass frequencies at a high level and without distortion of the transmitted sound. In the past, such bass frequencies have been distorted and almost completely lost while the higher frequencies were also adversely affected because of restriction of movement of the speaker. Tests have been run which have shown that the faithfulness of reproduction in the apparatus of this invention is extremely good at positions in which the bearer is located on the central axis of the speaker cone and at varying positions ranging from 30 off the axis to 60. The results of such tests are shown in Figure 6. These tests were made on the device of Figure 5 and other tests made on the modifications of Figures 1 to 4 showed similarly advantageous reproduction characteristics. In all such tests the bass frequencies running from 40 cycles to 200 cycles were reproduced at high sound levels and without distortion. This is to be compared with structures used in the past where the bass frequencies were almost completely lost and those that were heard were distorted. In addition the faithfulness of reproduction of the higher frequencies was found to be improved as a result of the pressure relief upon the speaker cone.

7 Various changes and modifications may be made within this invention as will be apparent to those skilled in the art. Such changes and modifications are within the teaching and scope of this invention as defined by the claims appended hereto.

What is claimed is:'

l. A loud speaker mounting means comprising a battle having an opening therein, a loud speaker mounted on said baffle over said opening, a cone diffuser mounted on said baffie opposite said opening, an enclosure means mounted on said bafiie containing said loud speaker and said bafiie having at least one pressure relieving opening therein outside said loud speaker.

2. A loud speaker mounting means comprising a bathe having an opening therein, a loud speaker mounted on said baflie over said opening, a cone diffuser mounted on said baffle opposite said opening, anenclosure means mounted'on said bafile containing said loudspeaker, said enclosure means comprising a frusto-conical extension of saidtbafiie extending rearwardly to a connection with a fiat wall and said bafile having at least one pressure relieving opening therein outside said loud speaker.

3. A loud speaker mounting means comprising a baflie having an opening therein, a loud speaker mounted on said baffle-over said opening, a cone diffuser mounted on said bafile opposite said opening, an enclosure means mounted on said batfie containing said loud speaker and said baflie having a plurality of concentric narrow pressure relieving arcuate openings therein outside said loud speaker.

References Cited in the file of this patent UNITED STATES PATENTS 6 Moore Oct. 19, 1937 Lowell Aug. 14, 1951 Shaffer Jan. 28, 1958 FOREIGN PATENTS Australia Aug. 4, 1936 OTHER REFERENCES Sweets File (Architectural) 1956 (Copyright Jan. 6, 1937 10 1956) (See. 32a L), pages 3, 4, and 7. 

